1. Field of the Invention
The present invention relates to a fuel sensor, which senses a property of fuel.
2. Description of Related Art
A fuel sensor is placed in a fuel supply system, which supplies fuel to an internal combustion engine. The fuel sensor senses a property of the fuel, such as an alcohol concentration of the fuel, a pressure of the fuel or an oxidation state of the fuel.
For example, WO 00/73646A1 (corresponding to U.S. Pat. No. 6,431,147B1) recites a fuel pressure regulator, which serves as a fuel sensor that senses the fuel pressure. This fuel pressure regulator includes a pressure detector portion that is placed in the fuel passage, through which the fuel discharged from the fuel pump flows. The fuel pressure regular controls an electric current, which is supplied to an electric motor of a fuel pump, based on a fuel pressure that is applied to the pressure detector portion.
In a case where the temperature of the fuel, which flows through the fuel passage, becomes high, and thereby the fuel pressure becomes lower than a saturation vapor pressure that corresponds to the temperature of the fuel, air bubbles are generated in the fuel. Furthermore, when the air bubbles, which are contained in the return fuel that is returned from the internal combustion engine to the fuel tank, are drawn into a fuel pump, the fuel, which contains the air bubbles, is discharged from the outlet of the fuel pump.
The fuel passage, which is provided in the fuel pressure regulator of WO 00/73646A1 (corresponding to U.S. Pat. No. 6,431,147B1), extends in the vertical direction. The pressure detector portion of the fuel pressure regulator is provided at an upper portion of the fuel passage in the vertical direction. Therefore, the air bubbles of the fuel may possibly be drawn into and stagnated in the pressure detector portion. When this happens, the pressure of the fuel cannot be accurately sensed with the pressure detector, thereby resulting in an sensing error of the fuel pressure.